Flame retarding and smoke retarding mixture

ABSTRACT

Flame retarding and smoke retarding aqueous solutions consisting essentially of: 70-96 weight % of a mixture of ammonium phosphate and ammonium sulphate, 1-20 weight % NaHCO 3 , 1-10 weight % EDTA, and water in an amount resulting in an aqueous solution comprising 11-45 weight % solids on the basis of the total weight of the aqueous solution. Methods of producing and using the flame retarding and smoke retarding aqueous solutions to impregnate absorbent porous materials, such as wood, rayon, cotton, wool and similar textile materials are also taught.

The present invention concern a flame retarding and smoke retardingmixture, a method for producing a solution of the mixture and theapplication of the mixture for treating materials that are normallycombustible.

Means are known how to apply different substances and mixtures to treatmaterials that are normally combustible to make them less combustibleand work as smoke retardants.

Different chemical compounds with flame retarding or smoke retardingcharacteristics are described in U.S. Pat. Nos. 4,168,175; 4,342,669 and4,438,028 and GB Patent Specification no. 1,462,828. None of themixtures described in these specifications give completely satisfactoryresults, since each mixture gives better results in one area than itdoes in other areas.

U.S. Pat. No. 4,595,414 describes the impregnation of cellulosematerials with a mixture of monoammonium phosphate, diammoniumphosphate, a freely-chosen corrosion inhibitor and a surfactant. Thismixture has subsequently been found to be most effective fornonflammable impregnation of cellulose textiles. The difficulty withsuch impregnation substances is that they give a relatively hard, stiffcellulose. Phosphates can also contain colourful contaminants.

U.S. Pat. No. 4,514,327 describes a fire retardant mixture consisting ofammonium sulphate, borax, boric acid and monoammonium phosphate. Thismixture will not supply wood with enough impregnation substance to meetthe Norwegian classification for a fire retardant. In the productionmethod filtration is mentioned through filters sized 5 micrometers,which will involve a very expensive process. Boric compounds such asborax and boric acid are also classified as health risks, partly becauseof the damage that can be done to the central nervous system. The use ofsuch compounds must thus be considered unfortunate both in theproduction process and when utilizing the product such as in impregnatedclothes. This patent specification does not cover the use of EDTA orNaHCO₃.

GB Patent Specification no. 2,165,270 describes a fire retardant mixtureconsisting of water-soluble monosodium phosphate, ammonium sulphate andborax and/or boric acid for the impregnation of porous materials. Asmentioned above, this compound will also represent a danger. Thisspecification does not mention the use of EDTA or NaHCO₃ to improve theimpregnation and the fire retardant characteristics.

DE Patent Specification no. 2,732,561 describes a mixture that consistsof ammonium ions, zinc ions, earth alkaline metal ions, chloride ions,bromide ions and phosphate ions. This patent specification also does notcover the use of EDTA or NaHCO₃ and the fire tests are not done inaccordance with any standard.

The main objective of the present invention is to produce a mixture thatgives better results than any existing known products for theimpregnation of materials that are normally combustible to prevent thecombustion of the treated materials, and prevent smoke developmentshould they be ignited or exposed to excessive heat.

A second objective of the present invention is to produce a mixture forthe impregnation of textiles made of materials such as rayon, cotton andwool, or other combustible, water-absorbent materials; and theimpregnation of wood, paper and other cellulose (wood) products, as wellas other organic materials.

A further objective with the present invention is to produce a nontoxicmixture that is neutral as far as color is concerned.

If a mixture is produced and used in accordance with the invention thiswill result in wood and textiles being impregnated to make themnonflammable and prevent smoke development should they be ignited orexposed to excessive heat.

The invention will now be described in more detail where reference willbe made to the figures, where

FIG. 1 shows the results from a technical fire test of spruce panelingimpregnated with a mixture in accordance with the invention, and

FIG. 2 shows the same as FIG. 1, but impregnated pine is used as thetest material.

The present invention has been developed to produce a mixture that issoluble in water for the treatment of materials that are normally arecombustible so as to act as a flame retardant and smoke retardant.

The mixture in accordance with the present invention is composed of:

70-96 weight % monoammonium phosphate and/or diammonium phosphate and/orammonium sulphate,

1-20 weight % NaHCO₃,

1-10 weight % EDTA,

0-28 weight % phosphoric acid (85%),

0-5 weight % normal additives.

The amounts given above are calculated in weight percentage on the basisof the total weight of the mixture. The mixture can contain less amountsof one or more additives such as surfactants, thickening agents,conservation agents or corrosion inhibitors.

The mechanism underlying the advantageous effect has not been completelyexplained. It is assumed that the following factors may be influential:

The addition of sodium hydrogen carbonate causes delayed migration andthe so-called beating of the dried mixture from the treated material, atthe same time as the treated material obtains a softer and smoothersurface.

The addition of sodium hydrogen carbonate also makes it easier to removethe air from the mixture according to the invention during theimpregnation process.

Sodium hydrogen carbonate in the mixture will give off CO₂ -gas whenheat is applied which will prevent the ignition of the material.

The addition of EDTA causes the contaminants in the components to beseparated by being soluble in water and becoming residue. The pH valueof the solution is to be from 3.50 to 9.00. A pH value between 6.70 and6.80 gives least corrosion and reduces the need for the addition ofcorrosion inhibitors for the impregnation of wood. After impregnationand drying EDTA acts as a lattice binding agent for mixtures thatthereby become more stable, at the same time as it acts as a flameretardant.

Production of a solution of such a mixture

A suitable amount of water is to be heated to between 30°-70° C. in anappropriate vessel and is kept at a stable temperature within theabove-mentioned limits during the entire mixing process. The mixingvessel should be made of stainless steel or plastic, and equipped with astirring device that gives good circulation in the liquid.

a) Ammonium sulphate is added to the water under constant stirring.Stirring continues until all the ammonium sulphate is dissolved, aminimum of 10 minutes stirring.

b) Mono- or diammonium phosphate is added to the mixture from step a)under constant stirring until all of it is dissolved, a minimum of 10minutes stirring.

c) The mixture from step b) has sodium hydrogen carbonate added in smallportions under constant stirring. The reaction in the mixture after theaddition of each portion of sodium hydrogen carbonate is to be completedbefore a new portion of sodium hydrogen carbonate is added.

d) EDTA is added under constant stirring until all of it is dissolved, aminimum of 10 minutes stirring. Thereafter the agitator is stopped andthe mixture is allowed to stand in the mixing vessel for 3-4 hours whilethe solid contaminants are allowed to precipitate. After this thesupernatant is filtered to remove particles with a diameter larger than100 micrometers (10 micrometers for the impregnation of wood).

The concentration of the mixture in the form of the solids in thesolution can be adjusted to the planned application of the solution,this can vary from 5 and 45 weight percentage of solids calculated onthe basis of the weight of the total solution.

Impregnation of wood

The impregnation of wood is best done in a conventional impregnationunit consisting of two horizontal, cylindrical tanks where one is abovethe other. The two tanks are connected by a pipe that has a valvefitted. The impregnation unit also consists of the equipment required toform a vacuum or pressurize the two tanks. A suitable unit for this isdescribed in NO Patent no. 155,835. In relation to the present inventionit is not necessary to describe the impregnation unit in more detail.

Wood that is to be impregnated is placed in the lower tank and the uppertank is filled with a solution of the mixture in accordance with thepresent invention. The impregnation process starts by the formation of avacuum in the upper and lower tanks to remove almost all the air fromthe tanks and the wood in the lower tank. When wood is to be treated,the solution must not contain particles with diameters greater than 10micrometers, and the solution must contain between 15 and 45 weightpercentage of solids calculated on the basis of the weight of the totalsolution.

Once almost all the air has been removed, the connection between the twotanks is opened to allow the solution from the upper tank to run intothe lower tank containing the wood. When the solution has run into thelower tank the valve seals the connection between the tanks and thelower tank is pressurized to about 12 bar for 1-4 hours. Then thepressure is released from the lower tank and the solution is drained.The wood is removed and dried in the conventional manner. Followingdrying, the wood is to be left with 15 to 30 weight percentage of themixture calculated on the basis of the weight that wood normally haswith a water content between 10-70% prior to impregnation.

Impregnation of textiles

Textiles made of materials such as rayon, cotton, wool, compoundtextiles or textiles of other combustible, water-absorbent materials,are dipped in the solution or sprayed by the solution. The concentrationof the solution will depend on the method of treatment and this willtypically be within a range from 5 to 20 weight percentage of solidscalculated on the basis of the weight of the total solution, whereparticles with a diameter larger than 100 micrometers are filtered away.When dipping, the excess liquid is squeezed out, then the textiles aredried, and after drying the textiles must show an increased weight ofbetween 10 and 15 per cent in the form of solids from the mixture.

Impregnation of paper and other paper products

Paper and paper products can be impregnated in the same way as textiles.

Technical fire tests

The effectiveness of the mixture has been demonstrated in technical firetests of three different materials: a) spruce paneling, b) pine and c)cotton curtains. Samples a) and b) were impregnated with the samemixture in accordance with the invention, produced in accordance withthe method described above, where the finished mixture had the followingconstituents:

    ______________________________________                                        ammonium sulphate       105    g                                              monoammonium phosphate  154    g                                              diammonium phosphate    105    g                                              EDTA                    28     g                                              NaHCO.sub.3             8.4    g                                              Water                   600    g.                                             ______________________________________                                    

The wood in a) and b) was impregnated in accordance with NO PatentSpecification no. 155,835, where a) was impregnated at 12 bar for onehour to give an absorption of impregnation agent of an average of 45weight %, based on the weight of the non-impregnated wood and the dryingredients in the impregnation mixture, and b) was impregnated at 12bar for two hours to give an average absorption of impregnation agent of43 weight %, based on the weight of the non-impregnated wood and the dryingredients in the impregnation mixture. After being dried in the normalway, samples a) and b) were subjected to technical fire tests inaccordance with Norwegian Standard NS-INSTA 412. The results arepresented in FIGS. 1 and 2.

The curtain, sample c), was impregnated by washing in a standard washingmachine, where the impregnation mixture consisted of:

    ______________________________________                                        water                   874.5  g                                              ammonium sulphate       22.8   g                                              monoammonium phosphate  87.4   g                                              EDTA                    5.0    g                                              NaHCO.sub.3             5.0    g                                              UFS75                   0.7    g                                              U6                      4.6    g.                                             ______________________________________                                    

The impregnation solution which here was supplied with a total weight of1000 g, had a content of 12.02 weight percentage dry constituents apartfrom the additives. The additive UFS75 is a softener that has ananti-static effect, U6 is an emulgator; both are from Unger Fabrikker inFredrikstad, Norway. The curtains were washed in the normal way, rinsedand spun, then the final rinsing program had the rinsing solutionreplaced by the above-mentioned impregnation solution. After spinningand drying, the curtains were supplied 12.7 weight % impregnation agent,based on the weight of the non-impregnated curtains and driedimpregnation agent. The curtains were then cut into smaller pieces andsubjected to technical fire tests in accordance with test method IMORes. 471 (XII). The results are given in the following table.

Test results

a) The results of the spruce paneling test are given in FIG. 1, thisshows that the impregnated spruce paneling satisfied the technical firespecifications in NS 3903 by a good margin, both with respect totemperature and performed exceptionally well concerning smokedevelopment, which is practically 0. After 10 minutes testing thetemperature was measured to be about 140° lower than the acceptabletemperature limit. During the entire test, there was no smokedevelopment of any note, this was well inside the acceptance criterion.

b) The results for pine show a little less resistance at the startcompared to spruce, but this evens out after about 6 minutes and, at theend of the test, pine gives a slightly better result than spruce. Thereis however more smoke density for pine than with spruce, neverthelessthe results for pine were within the technical fire test specificationsby a good margin.

c) The results from the technical fire tests for impregnated cottoncurtains are given below, where the product satisfies the stipulateddemands for resistance to ignition by flames in accordance with IMO Res.A. 471 (XII).

    ______________________________________                                               Ig-              Length of                                                                              Surface                                             nition  After-   burnt/carbon-                                                                          flaring                                                                              Ignition                              Burner time    flame    ized matter                                                                            Flames of cotton                             position                                                                             (s)     time (s) (mm)     (mm)   Yes/No                                ______________________________________                                        Surface                                                                               5      0        55       0      No                                    Surface                                                                              15      0        78       0      No                                    Edge    5      0        45       0      No                                    Edge   15      0        90       0      No                                    Edge   15      0        95       0      No                                    Edge   15      0        85       0      No                                    Edge   15      0        90       0      No                                    ______________________________________                                    

I claim:
 1. A method of applying a flame and smoke retarding aqueoussolution consisting essentially of: 70-96 weight % ammonium sulphate andammonium phosphates wherein the ammonium phosphates are selected fromthe group consisting of monoammonium dihydrogen phosphate and diammoniumhydrogen phosphate, the weight % of ammonium phosphates is greater thanthe weight % of ammonium sulphate, 1-20 weight % NaHCO₃, 1-10 weight %EDTA, and water in an amount resulting in an aqueous solution comprising11-45 weight % solids on the basis of the total weight of the solution,the method comprising the steps of impregnating a water absorbent porousmaterial, such as wood, rayon, cotton, wool and similar textilematerials in the solution to obtain saturation and then drying theimpregnated material to remove the water so as to leave the componentsof the flame and smoke retarding composition within the materials toreduce their ability to support a flame and produce smoke when a heatsource is applied.
 2. A flame and smoke retarding aqueous solutionconsisting essentially of:a) 70-96 weight % ammonium sulphate andammonium phosphates wherein the ammonium phosphates are selected fromthe group consisting of monoammonium dihydrogen phosphate and diammoniumhydrogen phosphate, the weight % of ammonium phosphates is greater thanthe weight % of ammonium sulphate; b) 1-20 weight % NaHCO₃ ; c) 1-10weight % EDTA; and d) the chemical composition is dissolved in apredetermined volume of water to obtain an aqueous solution having aconcentration of 11-45 weight % solids on the basis of the total weightof the solution.
 3. A method for producing an aqueous solution of aflame and smoke retarding composition consisting of 70-96 weight %ammonium sulphate and ammonium phosphates wherein the ammoniumphosphates are selected from the group consisting essentially ofmonoammonium dihydrogen phosphate and diammonium hydrogen phosphate, theweight % of ammonium phosphates is greater than the weight % of ammoniumsulphate, 1-20 weight % NaHCO₃, 1-10 weight % EDTA, and water in anamount resulting in a mixture comprising from 11-45 weight % solids onthe basis of the total weight of the solution, the method comprising thesteps of:a) heating the water in a mixing vessel to a temperature from30° C. to 70° C., thereupon holding this temperature constant throughoutthe procedure of dissolving the mixture; b) adding the ammonium sulphateto the heated water from step a, under constant stirring, until all ofthe ammonia sulphate is dissolved; c) adding the ammonium phosphate tothe mixture, under constant stirring, until all of the ammoniumphosphate is dissolved; d) adding the sodium hydrogen carbonate (NaHCO₃)to the mixture in small portions under constant stirring, this additionis to be performed in portions so that the reaction in the mixture afterthe addition of each portion of sodium hydrogen carbonate is completedbefore a new portion is added; e) adding the EDTA, under constantstirring, until all of it is dissolved in the solution, whereupon theheating is stopped and the mixture is allowed to stand and cool withoutstirring in the mixing vessel for a period of time so that the solidcontaminants are allowed to precipitate; and f) decanting and filteringthe supernatant from step e so as to remove particles having a diameterlarger than 100 micrometers.
 4. The method as described in claim 3wherein the composition is stirred in steps b, c and e a minimum of tenminutes and the mixing vessel is allowed to cool for at least 3-4 hoursto allow precipitation of the solid contaminants.
 5. The method asdescribed in claim 3, wherein the particles having a diameter largerthan 10 micrometers are removed by the filtering step so that theaqueous solution can be used to impregnate wood.